The present invention relates generally to operations involving tools, such as safety valves, etc., installed in subterranean wells and, in an embodiment described herein, more particularly provides apparatus and methods for achieving secondary lock-out of such safety valves.
It is sometimes desired to lock-out a safety valve, that is, to prevent closure of the safety valve, after it has been installed in a subterranean well. Among the reasons for locking-out the safety valve may be that the safety valve has ceased to function properly, or operations are to be performed through the safety valve and its closure during those operations is to be prohibited. If the safety valve is malfunctioning, the lock-out operation may also establish fluid communication between a control line attached to the safety valve and extending to the earth's surface, and a second, typically wireline-conveyed, safety valve subsequently landed in the malfunctioning safety valve. This operation, in which a safety valve is prevented from closing and fluid communication is established with the safety valve's control line, is sometimes referred to as a "primary" lock-out.
In another type of lock-out, a second control line-operated safety valve is not to be installed, so it is not necessary or desired to establish fluid communication with a control line. This operation, in which a safety valve is prevented from closing, but fluid communication is not established with the safety valve's control line, is sometimes referred to as a "secondary" lock-out. Another safety valve which does not use control line pressure in its operation, such as a tubing-pressure or velocity-type safety valve, may or may not be subsequently installed to replace the locked-out safety valve. In any event, such secondary lock-out operation permits remedial operations to be performed in the well, without the danger of the safety valve inadvertently closing on a wireline, coiled tubing, or during an acidizing treatment, etc.
Some safety valves, such as the SP-1.TM. safety valve manufactured by, and available from, Halliburton Energy Services of Duncan, Okla., are initially equipped with built-in features that facilitate convenient lock-out operations. However, other safety valves, such as Halliburton Energy Services' WELLSTAR.RTM. safety valve, do not include such features and, thus, a lock-out operation for these safety valves typically involves use of a specially designed tool. The tool is usually positioned within the safety valve and a mechanism of the tool is actuated to prevent closure of the safety valve.
One type of specially designed tool used for secondary lock-out of a safety valve deposits an expandable ring within the safety valve, in order to maintain a flapper of the safety valve in an open position. The expandable ring is deposited within the safety valve so that the ring contacts the flapper and overcomes the biasing force of a spring acting to close the flapper. Unfortunately, due to design restrictions of the tool, the ring is very thin in cross-section and, thus, potentially weak and unreliable, the ring may extend inwardly into an axial flow passage of the tool and interfere with subsequent operations therein, and the ring is susceptible to damage and dislodgement if the safety valve is inadvertently operated by applying fluid pressure to its control line.
Another type of specially designed tool used for secondary lock-out of a safety valve deposits an expandable ring within the safety valve between an opening prong of the valve and an internal shoulder to thereby prevent the opening prong from displacing to a position in which the valve will be permitted to close. The tool is latched into the opening prong and tubing pressure is applied to a tubing string attached above the safety valve in order to displace the opening prong to a position in which the valve is open, and then to deposit the expandable ring. Unfortunately, it is possible for the ring to be deposited in the wrong location since it is latched to the movable opening prong and a shear pin which determines the pressure at which the ring is deposited may shear before the opening prong has been fully displaced to the open position. Additionally, due to design restrictions, the ring is very thin in cross-section and weak.
From the foregoing, it can be seen that it would be quite desirable to provide an apparatus for achieving lock-out of a safety valve which does not utilize a thin or weak expandable ring and which is not located relative to a moveable point of reference during its operation, but which prevents closure of the safety valve by depositing an expandable ring within the valve. Additionally, it would be desirable to provide an expandable ring for use with the apparatus that is structurally sound in axial compression, but that is capable of significant radial expansion and contraction. Furthermore, it would be desirable to provide the apparatus with features that prevent deposition of the ring when the apparatus is not actuated properly, enable the ring to be safely retrieved with the apparatus in the event that the apparatus has been only partially, or improperly, actuated, and which indicate upon retrieval to the earth's surface whether the apparatus has been properly actuated. Methods of achieving lock-out of a safety valve which ensure convenient and reliable operations in preventing closure of the safety valve would also be desirable.
Still further, it would be desirable to provide an apparatus which is capable of depositing a radially displaceable ring with respect to any of a variety of downhole tools. For example, tools such as packers, sliding side doors, plugs, etc. may have one or more members disposed therein which are displaceable to set or unset, open or close, or otherwise operate the tools. Such an apparatus may be used to limit displacement of these members. Alternatively, the deposition of a radially displaceable ring relative to a downhole tool may be used for other purposes, for example, to centralize a packer, plug, etc. within a wellbore prior to setting it therein.